This invention relates to oil shale, and more particularly, to a surface retorting and disposal process.
Researchers have now renewed their efforts to find alternate sources of energy and hydrocarbons in view of past rapid increases in the price of crude oil and natural gas. Much research has been focused on recovering hydrocarbons from solid hydrocarbon-containing material such as oil shale, coal and tar sands by pyrolysis or upon gasification to convert the solid hydrocarbon-containing material into more readily usable gaseous and liquid hydrocarbons.
Vast natural deposits of oil shale found in the United States and elsewhere contain appreciable quantities of organic matter known as "kerogen" which decomposes upon pyrolysis or distillation to yield oil, gases and residual carbon. It has been estimated that an equivalent of 7 trillion barrels of oil are contained in oil shale deposits in the United States with almost sixty percent located in the rich Green River oil shale deposits of Colorado, Utah and Wyoming. The remainder is contained in the leaner Devonian-Mississippian black shale deposits which underlie most of the eastern part of the United States.
As a result of dwindling supplies of petroleum and natural gas, extensive efforts have been directed to develop retorting processes which will economically produce shale oil on a commercial basis from these vast resources.
Generally, oil shale is a fine-grained sedimentary rock stratified in horizontal layers with a variable richness of kerogen content. Kerogen has limited solubility in ordinary solvents and therefore cannot be recovered by extraction. Upon heating oil shale to a sufficient temperature, the kerogen is thermally decomposed to liberate vapors, mist, and liquid droplets of shale oil and light hydrocarbon gases such as methane, ethane, ethene, propane and propene, as well as other products such as hydrogen, nitrogen, carbon dioxide, carbon monoxide, ammonia, steam and hydrogen sulfide. A carbon residue typically remains on the retorted shale.
Shale oil is not a naturally occurring product, but is formed by the pyrolysis of kerogen in the oil shale. Crude shale oil, sometimes referred to as "retort oil," is the liquid oil product recovered from the liberated effluent of an oil shale retort. Synthetic crude oil (syncrude) is the upgraded oil product resulting from the hydrogenation of crude shale oil.
In surface retorting, oil shale is mined from the ground, brought to the surface, crushed and placed in vessels where it is contacted with a hot solid heat carrier material, such as hot spent shale, ceramic balls, metal balls, or sand or a gaseous heat carrier material, such as light hydrocarbon gases, for heat transfer. The resulting high temperatures cause shale oil to be liberated from the oil shale leaving a retorted, inorganic material and carbonaceous material such as coke. The carbonaceous material can be burned by contact with oxygen at oxidation temperatures to recover heat and to form a spent oil shale relatively free of carbon. Spent oil shale which has been depleted in carbonaceous material is removed from the retort and recycled as heat carrier material or discarded. The combustion gases are dedusted in cyclones, electrostatic precipitators, or other gas-solid separation systems.
During retorting, voluminous amounts of retorted oil shale and retort water are produced which create significant processing and disposal problems. Retorted oil shale and retort water contain numerous impurities (pollutants). For example, the impurities in combusted shale include silicon, aluminum, calcium oxides, and various sulfates. The impurities in non-combusted retorted shale include numerous organic and inorganic compounds and various oxides. The impurities (contaminants) in retort water include shale oil, carbonates, phenol, soluble organic carbon, ammonia, and oil shale particulates. Furthermore, retort water, as well as combusted and retorted shale, often contain various trace metals and materials, such as cyanide, arsenic, etc., which in sizeable quantities can be detrimental and hazardous to the safety and health of animal and plant life in nearby bodies of water and the surrounding environment. The above impurities must be prevented from leaching into the ground and polluting underground aquifers and nearby rivers, streams, and ponds. While some of the retorted shale can be used for backfilling spent modified-in-situ underground retorts or to produce cement for roadways or the like, and some of the contaminated retort water can be recycled for other uses in the process, sizeable quantities of retorted oil shale and retort water still must be treated and/or disposed of in an environmentally acceptable manner.
Over the years, various methods have been suggested for controlling leaching and seepage at disposal sites. These methods typically include a waterproof impermeable barrier or liner made of metal, cement, plastic, or asphalt. Typifying these methods and various methods to process spent shale are described in U.S. Pat. Nos. 2,592,468; 2,904,445; 3,108,441; 3,135,618; 3,394,551; 3,405,528; 3,405,529; 3,459,003; 3,625,010; 4,047,387; 4,096,912; 4,120,355; 4,131,416; 4,154,549; 4,198,097; 4,231,617; 4,315,656; 4,320,994; 4,375,985; 4,377,465; and 4,415,365. These prior art methods have met with varying degrees of success.
It is therefore desirable to provide a process which overcomes many, if not most, of the above problems.